Method of operating and apparatus for watercraft



July 17, 1962 G. J. WENNAGEL ETAL 3,044,432

METHOD OF OPERATING AND APPARATUS FOR WATERCRAFT Filed. D90. 2, 1959 2 Sheets-Sheet l INVENTORS GLENFORD J. WENNAGEL ROBERT R. GILRUTH ATTORNEY July 17, 1962 G. J. WENNAGEL ETAL 3,044,432

METHOD OF OPERATING AND APPARATUS FOR WATERCRAFT Filed Dec. 2, 1959 2 SheetsSheet 2 INVENT 8 GLENFORDJ. WENNA L B OBERT R. GILRUTH ATTORNEY nited States This invention relates to watercraft, and more particularly to hydrofoils for high-speed watercraft and to a method of operating such watercraft to attain even greater speeds.

When hydrofoils are operated at high speeds, vapor bubbles form along the upper surface of the foil and collapse haphazardly and explosively on that surface thereby causing vibration and damage to the foil, as well as adversely afiecting the lift-drag characteristics of the foil. The bubbles form vapor cavities over the upper surface of the hydrofoil, and this phenomenon is termed cavitation. If the flow conditions are such that one large cavity is formed over the entire upper surface of the hydrofoil, such flow is termed supercavitating flow, while those conditions encountered at speeds below that at which cavitation occurs are termed subcavitating flow.

It is an object of the present invention to provide a hydrofoil with means for forming over the upper surface thereof a vapor cavity of such magnitude that the vapor bubbles do not collapse on the upper surface, but are carried beyond the trailing edge of the foil to collapse harmlessly in the Water aft-of the foil.

It is an object to provide a hydrofoil with means for controlling the inception of or inducing such cavity flow to thereby control the transition from subcavitating to supercavitating flow conditions. Further thereto, it is an object to provide a hydrofoil with flap means for controlling the transition from subcavitating to supercavitating flow conditions.

It is a further object to provide a hydrofoil with means to vary the load characteristics of the foil during and after transition from subcavitating flow to supercavitating flow conditions.

It is a further object to provide a hydrofoil with a pivotally mounted trailing edge section which functions as a lift control device at slow speeds, but which is adapted to be retracted within the boundaries of the cavity at high speed operation to thereby reduce the 'wetted area of the foil and hence its drag.

It is a still further object to provide a method of operating a watercraft provided with such hydrofoils.

Other objects of the invention, as well as the advantages thereof, will become apparent from the following description when considered in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a hydrofoil embodying the present invention;

FIG. 2 is a section of the hydrofoil showing in broken lines the operating positions of the different surfaces;

'FIG. 3 is a section of the hydrofoil showing the flow lines thereabout when operating under subcavitating flow conditions;

FIG. 4 is a section of the hydrofoil showing the flow lines thereabout when operating under conditions similar to those of FIG. 3;

FIG. 5 is a section of the hydrofoil showing the flow Patented July 17, 1962 lines thereabout when operating under controlled or induced supercavitating flow conditions;

FIG. 6 is a section of the hydrofoil showing the flow lines thereabout when operating under supercavitating flow conditions; and

FIG. 7 is a diagrammatic sectional view showing means suitable for operating the trailing edge section.

Referring to the drawings, and particularly FIG. 1 thereof, there is shown in broken lines a portion of the port side of a hull 10 upon which is mounted a strut member 11 which in turn mounts on the lower end thereof a hydrofoil 12 constructed in accordance with the present invention. A similar strut and hydrofoil, not shown, is mounted on the starboard side of the hull 1t) and although the hydrofoil 12 is shown to be of substantially delta planform, no significance is to be attached thereto for the present invention is equally applicable to hydrofoils of different planforms.

Still referring to FIG. -1, and also now to FIG. 2, the hydrofoil 12 is shown to comprise a main body portion 13 provided with a lift control surface 14 pivotally mounted to the rear portion thereof, which surface 14 is adapted to be deflected upwardly and downwardly and lowered to a position below the main body portion 13, all as shown in FIG. 2. The hydrofoil is provided also with pivotally mounted leading edge flaps 15, one on either side of the center thereof, and a pivotally mounted undersurface flap 16, all of which flaps are adapted to be deflected from positions in which they fair with the upper and lower surfaces of the main body 13 to the dotted line positions shown in FIG. 2. It will be noted that the hydrofoil 12 is of a relatively thin cross-sectional shape having a concave bottom surface and a sharp leading edge.

The subcavitating flow condition of operation of the hydrofoil is shown in FIG. 3. As shown by the dotted lines therein, the lift control surface 14 may be deflected upwardly or downwardly to vary the camber of the foil to thereby vary its lift characteristics. Under similar conditions of operation, the surface 14 may be lowered to the position shown in FIG. 4, in which position it again may be deflected upwardly or downwardly, or the undersurface flap 16 may be extended to the dotted line position shown to vary the lift characteristics of the hydrofoil.

To control the inception of or to induce supercavitating flow at speeds less than those at which such flow would normally occur, the flap 15 may be defiected upwardly as shown in FIG. 5. It will be noted that the cavity thereby created extends beyond the trailing edge of the foil whereby the vapor bubbles collapse in the water aft of the hydrofoil. During such operation, the control surface 14 or the flap 16 may be deflected to vary the lift of the foil, or the control surface 14 may be retracted completely within the boundaries of .the cavity as shown to reduce the wetted area of the foil to thereby reduce the drag, and by so doing, to improve the lift-drag characteristics of the foil. 7

In FIG. 6, the hydrofoil is shown operating at a speed sufficient to create a cavity without the aid of the flap 15, which cavity is shown to extend beyond the trailing edge of the foil. During such operation, the control surface 14 or the flap 16 may be deflected to vary the lift characteristics of the foil, or the surface 14 may be retracted completely within the boundaries of the cavity as shown to again reduce the wetted area and hence the dragof the hydrofoil.

FIG. 7 illustrates, more or less diagrammatically, means extensions or arms 20 to which are pivotally attached at V the upper extremities thereof forwardly extending links 21. Actuating means, not shown, connect to the links 221.

A pulley or sheave 22 is keyed or otherwise aflixed to the torque tube 17 and is connected by means of an endless cable 23 to a pulley or sheave 24 rotatably mounted upon the cross pin 19. The pulley 24 is actuated by a cable 25 which leads to any suitable control device provided in the hull. As may be dictated by practical considerations, sprockets and chains or levers and push-pull rods may be substituted for the pulleys 22 and 24 and the cables 23 and 25 shown.

It is readily apparent that motion of the cable -25 causes rotation of the pulley 24 which in turn, through the endless cable 23, causes rotation of the pulley 22 and the torque tube 17 afiixed thereto, to thereby deflect upwardly or downwardly the control surface 14. Aft movement of the link 21 by the actuating means not shown causes clockwise rotation of the supporting members 18 about the cross pins :19. If the pulley 24 is held against rotation by the cable 25 at such time, the control surface 14 as it moves downwardly will be rotated in a counterclockwise direction about the axis of the torque tube 17 where by the angular relationship between the main body portion 13 and the control surface 14 will remain substantially unchanged as the control surface 14 is lowered to the position shown in FIG. 4.

The normal sequence of operation of a watercraft provided with hydrofoils of the present invention may comprise the following steps:

Operation with the flaps '15 and 16 retracted and actuation of the surface 14 to vary loading at low speeds as shown in FIG. 3; lowering of the surface 14 and deflection of the flap 16 or actuation of the surface 14 to vary loading at low-to-intermediate speeds as shown in FIG.

4; deflection of the flap 15 to induce supercavitating flow as the speed increases to that at which uncontrolled or destructive cavitation wouldotherwise begin to occur,

and deflection of the flap -16 or actuation of surface 14 to vary the loading, or retraction of the surface 14 within the boundaries of the cavity to reduce the wetted area as shown in FIG. 5; and finally, retraction of the flap 15 and actuation of the surface 14 orthe flap 16 to vary the load ing, or retraction of the surface 14 within the boundaries of the cavity as shown in FIG. 5 when the speed becomes suflicient to create a full cavity without the aid of the flap 15.

Thus, there is provided apparatus for and a method of operating a watercraft provided with hydrofoils to induce supercavitating flow at speeds less than those at which such flow would normally occur and to reduce the drag of the hydrofoils by retracting associated lift control surfaces within the boundaries of the cavity so formed or within the boundaries of the cavity formed by normal high-speed operation of the hydrofoils.

Although shown and described in what is believed to be the most practical and preferred embodiment, it is apparent that departures therefrom will suggest thernselves to those skilled in the art and may be made without departing from the spirit and scope of the invention. -We therefore do not Wish to. restrict ourselves to the particular form of construction illustrated and de-- cave bottom surface and a sharp leading edge, and a 4' leading edge flap pivoted to the upper surface thereof and adapted to be extended to induce cavity fiow around the hydrofoil.

2. A hydrofoil comprising a main body having a concave bottom surface and a sharp leading edge, a leading edge flap pivoted to the upper surface of said main body and adapted to be extended to induce cavity flow around the hydrofoil, and a lift control surface pivoted tothe rear portion of said main body and adapted to be retracted within the boundaries'of the cavity to reduce the wetted area of the hydrofoil.

3. A hydrofoil as set forth in claim 2 wherein said lift control surface is adapted also to be lowered to a position below said main body.

4. A hydrofoil comprising a main body having a concave bottom surface and a sharp leading edge, a fiap pivoted to the lower rear portion of said main body and adapted to be extended to vary the lift characteristics of the hydrofoil, and a lift control surface pivoted to the rear portion of said main body aft of said flap and adapted to be retracted within the boundaries of the cavity-formed above the hydrofoil at high-speed operation thereof.

5. A hydrofoil comprising a main body having a concave bottom surface and a sharp leading edge, a leading edge flap pivoted to the upper surface of said main body and adapted to be extended to induce cavity flow around the hydrofoiL'and a flap pivoted to the lower rear portion of said main body and adapted to be extended to vary the lift characteristics of the hydrofoil.

6. A hydrofoil comprising a main body having 'a concave bottom surface and a sharp leading edge, a leading edge flap pivoted to said main body and adapted to be extended to induce cavity flow around the hydrofoil, a flap pivoted to the lower rear portion of said main body and adapted to be extended to vary the lift characteristics of the hydrofoil, and a lift control surface pivoted to the rear portion of said main body aft of said second mentioned flap, said lift control surface adapted to be retracted within the boundaries of the cavity to reduce the wetted area of the hydrofoil.

7. The method of operating a watercraft having hydrofoils provided with leading edge flaps and lift control surfaces, which comprises adjusting the position of said flaps to induce cavity flow around the hydrofoils, and retracting the control surfaces within the boundaries of the cavities to reduce the wetted area of the hydrofoils.

' 8. The method of operating a watercraft having hydrofoils provided with undersurface flaps and a trailing edge mounted control surface which comprises driving the craft at a speed sufiicient to produce cavity flow around the hydrofoils, retracting the control surfaces Within the boundaries of the cavities so produced to reduce the wetted area of the hydrofoils, and adjusting the position of said undersurface flaps to vary the lift characteristics of the hydrofoils.

9. The method of operating a watercraft having hydrofoils provided with leading edge and undersurface flaps and a trailing edge mounted control surface, which comprises adjusting the position of said leading edge flaps to induce cavity flow around'the hydrofoils, retracting the control surfaces within the boundaries of the cavities to reduce the wetted area of thehydrofoils, and adjusting the position of said undersurface flaps to vary the lift characteristics of the hydrofoils.

10. The method of operating a Watercraft having'hydrofoils provided with leading edge and undersurface flaps and a trailing edge mounted control surface, which comprises adjusting the position of saidleading edge flaps to induce supercavitating flow as the speed of the craft increases to that at which destructive cavitation beings to occur, retracting the control surfaces within the boundaries of the cavities to reduce the wetted area of the hydrofoils, and retracting said leading edge flaps to a position in which they fair with the upper surface of the hydrofoils as the speed of the craft is increased to that sufficient to produce supercavitating flow with said leading edge flaps in said faired position.

References Cited in the file of this patent UNITED STATES PATENTS 5 Re. 19,651 Congdon July 23, 1935 Re. 24,099 Maxwell Dec. 6, 1955 1,964,418 Alfaro June 26, 1934 2,257,406 Burtenbach Sept. 30, 1941 2,350,809 Pelessoni June 6, 1944 10 6 Zuck Jan. 16, 1951 Zobel July 31, 1951 Hill et a1 Mar. 2, 1954 Gilruth -5 Mar. 1, 1955 Schertel Nov. 20, 1956 Barkla Aug. 27, 1957 Boericke. June 16, 1959 FOREIGN PATENTS Switzerland Nov. 16, 1931 

